Electric resistances



Patented Aug. 4, 1953 ELECTRIC RES-ISTANCES Erich Weides, Langel, near Porz (Rhine), Germany No Drawing.

rial No. 199,555. 1949 1 Claim.

This invention relates to an electric resistance consisting of a resistance carrier made of dense insulating material, for example ceramic material, to which a resistance layer of carbon, badly-conductive metal, a metal compound or of semi-conductive glaze is applied. In order to protect the resistance layer against mechanical injury and also chemical and physical influences it has hitherto received a coating of a varnish, a synthetic resin or of some cast compound. Coatings have also been given to the resistance by pressing round it and spraying round it synthetic resin or tubes of insulating material. In the known resistances, furthermore, the entire resistance was placed in a strong protective tube of a synthetic material, glass or ceramic material.

These protective measures can only be imperfect because it is found that synthetic resin coats, even if not hygroscopic, are permeable to water vapour; tube coatings show fine cracks and microscopic channels. All coatings of organic substances are sensitive to temperature and are unserviceable at a surface temperature of more than 300 C. Solid protective tubes hinder the necessary dissipation of heat owing to their great heat insulation.

These drawbacks are avoided according to the invention according to which the protective layer is made of inorganic insulating material with a heat conductivity of more than 1.5 K cal/hm C. between and 100 C. An insulating material of this kind is, for example, a hardenable cement of an inorganic basis. This cement can, for example, be produced as follows:

280 gr. of porcelain, steatite, sillimanite or mullite in the form of sand of a grain size below 0.1 mm. are stirred with 100 cos. of a solution of aluminium phosphate, phosphoric acid and water into a sprayable and coatable mixture. This cement hardens very quickly after being applied to the resistance layer of the carrier body. For good radiation of heat and identification purposes there may also be applied to the Application December 6, 1950, Se-

In Germany December 6,

protective layer a thin colour coat, for example, of ferric oxide. The protective layer is heatproof up to 600 C.

The resistance layer consists of carbon and is suitably produced by the separation of carbon from gaseous hydrocarbons.

Caps, rings or soldered lugs may serve as contact pieces. These may also be covered with the protective layer as far as the parts serving for contact.

The resistance according to the invention has the advantage over known constructions that, owing to its good dissipation of heat, the permissible nominal load can be increased many times as compared with known resistances of equal dimensions. As it is almost free from inductive effects it can also be eifectively used as a cathode resistance and R-C member.

I claim:

An electric resistance comprising a carrier body of insulating material, a resistance layer applied to the carrier body, said resistance layer being covered by a protective layer consisting of hardenable cement, characterized therein that the cement consists of a mixture of phosphoric acid, aluminum phosphate, and ceramic materials of the group comprising porcelain, steatite, sillimanite, mullite, the relative proportions of aluminum phosphate and phosphoric acid being so chosen that a heat conductivity of more than l.5 K cal/hm C. between 20 and C. re-

sults.

ERICH WEIDES.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,405,449 Robinson Aug. 6, 1946 FOREIGN PATENTS Number Country Date 462,781 Great Britain Mar. 16', 1937 

